16.5 CHAPTER 16. OPTICAL PHENOMENA; PROPERTIES OF MATTER
As the photons bouncebetween mirrors, they continually pass throughthe laser ma-
terial, stimulating thoseatoms to emit more photons. This creates an ever increasing
beam of photons, all with the same characteristics, all travelling in the same direc-
tion. In this way, the optical cavity helps to amplify the original laser photons into a
concentrated, intense beam of photons.
The laser cavity also helps to narrow the frequency range of laser lightemitted. The
distance between the two mirrors defines the cavity mode which only allows lightof a
narrow range of frequencies to continue being reflected back and forth.Light of other
frequencies damped out. (This is just like in thechapter on the physics of music where
a pipe of a certain length corresponds to a particular wavelength of sound.) Therefore
only a narrow frequencyof light can be emitted.
Laser applications and safety ESCHQ
Although the first working laser was only produced in 1958, lasers are now found
in many household items. For example, lasersare well-known throughtheir use as
cheap laser pointers. However, lasers can be very dangerous to the human eye since a
large amount of energyis focused into a very narrow beam. NEVER POINT A LASER
POINTER INTO SOMEBODY’S EYES - IT CAN BLIND THEM FOREVER.
Other uses include:
- Semiconductor lasers which are small, efficientand cheap to make areused in
CD players. - He-Ne Lasers are usedin most grocery shops toread in the price of items using
their barcodes. This makes the cashiers’ job much quicker and easier. - High energy lasers areused in medicine as acutting and welding tool. Eye
surgery in particular make use of the precision of lasers to reattach the retinas of
patients’ eyes. The heat from cutting lasers also helps to stop the bleeding of a
wound by burning the edges (called cauterising).
See simulation: Vpqof at http://www.everythingscience.co.za)